Nonwoven mat wet forming machines having a moving, inclined forming wire are known for making all kinds of nonwoven mats from a low concentration of fibers dispersed in a normally aqueous whitewater and it is known to use such machines as manufactured by Voith GmBh, Sandy Hill Corp. and others. Nonwoven mats are used as substrates in the manufacture of a large number of products including roofing of all types, carpet, etc. and also as a facing for products like wallboard, foam board and insulation. Methods of making nonwoven mats using wet laid processes on such machines are described in U.S. Pat. Nos. 4,112,174, 4,681,802, and 4,810,576, the disclosures of which are hereby incorporated herein by reference. In these processes a slurry of glass fiber is made by adding fiber to a typical white water in a pulper to disperse the fiber in the white water forming a slurry having a very low fiber concentration to feed to the above machines where the fibers are deposited on the moving forming wire, a permeable, moving belt, to form a wet web. Excess water is removed from the slurry on the forming wire using one or more suction tube assemblies located beneath the moving forming wire. The dewatered, but still wet, nonwoven web of fiber is then usually transferred to a second moving screen in-line with the forming screen and run through a binder saturating station where an aqueous binder mixture, such as an aqueous acrylic resin based binder mixture, is applied to the mat in any one of several known ways. The mat, saturated with the binder, is then run over one or more additional suction tube assemblies while still on the second moving screen to remove excess binder.
The wet mat is then transferred to a moving wire mesh belt, or a honeycomb drum, and run through an oven to dry the wet mat and to cure (polymerize) the resin based binder to bond the fibers together in the mat. Preferably, the aqueous binder solution is applied using a curtain coater or a dip and squeeze applicator, but other methods of application such as spraying are also known.
In the drying and curing oven the mat is subjected to temperatures up to 450 or even 550 degrees F. or higher for periods usually not exceeding 1-2 minutes and as little as a few seconds.
The wet forming machines have gotten wider and are being run fastest and faster to increase productivity. Due to the low concentration of the fiber slurry, about 0.005 to about 0.02 percent, use a very large pumps to feed the fibrous slurry to the forming box or boxes because of the high degree of dilution needed to keep the fibers well dispersed and to achieve the degree of uniformity of fibrous structure needed for the end use of the nonwoven mats. Therefore, more and more water, and aqueous binder, must be removed by the suction tube assemblies in the forming section and in the binder application section(s) of the wet forming line. On existing machines, the productivity of the mat lines is being hampered by having to shut the machine down to clean lodged fibers from the slots of the suction tubes, fibers that have been passed through the openings in the forming wire. Also, as fiber lodges in the suction slot of the suction tube, this interference begins to vary the basis weight and/or binder content of the mat across the width of the mat. These problems are particularly troublesome when making roofing products or other mats that use longer fibers because the longer fibers tend to hang-up over or around the open slot that is close to or kisses the bottom side of the forming wire. Also, since most of the volume of nonwoven mats is for roofing and roofing being very seasonal with mat inventory being relatively low density and very bulky, an increased mat capacity per line, per crew, per location, etc. would also provide a significant competitive advantage during the peak demand times.